Efficient access to chiral benzo[c]chromenes via asymmetric transfer hydrogenation of ketals

Abstract

A highly enantioselective synthetic method to access chiral α-substituted 6H-benzo[c]chromenes through chiral imidodiphosphoric acid-catalyzed asymmetric transfer hydrogenation of the corresponding ketals has been established. The substituent patterns at the α-position proved to be unsusceptible to the asymmetric catalysis system, with diverse hybrid substituents including aryl and vinyl, alkynyl, and alkyl moieties that were well tolerated. In addition, the generality of the method was further demonstrated by application to 1H-isochromene-based ketals, offering chiral α-aryl and -alkyl 1H-isochromenes in excellent ee.